1. Field of the Invention
The present invention is for an apparatus and a method for anticipating disk burst failures in turbo-machinery blades. The apparatus comprises at least one blade tip sensor for sensing blade passage making measurements of blade tip time-of-arrival and clearance from the sensor to a blade tip and a computer for compilation and analysis of data from the sensor.
2. Description of the Related Art
If they are not replaced, turbo-machinery disks (spinning hubs and blades) eventually burst due to spin-induced inertial forces and fatigue. The failure pattern varies but is always marked by growth in the diameter of the disk during disintegration. Moreover, such growth is not uniform, but rather biased due to asymmetric crack propagation in the disk.
Historic methods to predict disk failure rely on standard materials analysis, including x-ray crystallography, sonograms, and other diagnostic techniques, after the turbo-machinery is disassembled. The predictive value relies on estimating when micro-cracks have formed and then searching for confirmation. Due to wide variations in operating conditions and in the fatigue life of turbo-machinery components, historic-methods require frequent inspection intervals-to maintain safe operation.
A recent experimental technique employed in spin pit analyses relies on changes in the imbalance when a suspended turbo-disk is spun on a quill shaft. The reasoning behind this technique is that crack propagation will progressively shift the imbalance in the rotating disk. This technique may have applications in controlled experiments in spin pits, but may be-difficult to apply in engine operation, where many effects cause shifts in imbalance.
Disk diameter can be monitored at the blade tips at the outside edge of the disk. For example, in a turbine with N blades, a blade clearance sensing system provides N measures of rotor radius for every engine revolution. The trend of such measurements over many operational cycles can reveal a local bulge or bulges indicative of impending disk burst.
The diameter expands elastically as the disk is spun to high rpm and contracts again when the disk is slowed. Such xe2x80x9celastic stretchxe2x80x9d can create a relatively large signal, roughly equal for each blade on the spinning disk. The detection system must discount this form of stretch. One way to do so is to compare disk diameter during each operating cycle at the same rpm, so as to detect only variations due to causes other than elastic stretch.
An additional complication is the variation due to temperature, which can also add significant increases to the diameter. This too can be disregarded by comparing diameter at constant temperature or by comparing each blade to the average of all blades.
It is an object of the present application to present an apparatus and method for anticipating disk burst failures in turbo-machinery which uses one or more case-mounted sensors observing blade passage and interpreting these measurements by searching for unusual deformation of one or a few of the blades.